The present invention generally pertains to the field of continuous oven cooking systems for performing continuous oven cooking processes on continuous lines of food items. In particular, it pertains to a controller for such a system that provides on-line handling of a deviation in a scheduled parameter during the continuous oven cooking process by identying any food items that will be under cooked as a result of the deviation.
A continuous oven cooking system is a continuous source food processing system. This system is widely used in the food preparation industry to cook food items, particularly meat items, in mass quantities. Such a system includes an oven through which a continuous line of the same type of food items {1, . . . , i, . . . , I}line is conveyed by a belt. The oven includes one or more zones to cook the food items. Each zone may have a corresponding scheduled environment temperature, a corresponding scheduled air circulation velocity, and a corresponding scheduled relative humidity. The belt has a scheduled belt speed for conveying the food items through the oven.
Each food item i must be commercially cooked during the continues oven cooking process in such a way that is free from pathogens, such as E. coli, Listeria monocytogens, and Salmonella spp. Under USDA (U.S. Department of Agriculture) and/or FDA (Food and Drug Administration) regulations, this can be achieved using one or both of two different approaches.
The first approach is to ensure that the final core temperature Tc(te,i)i of each food item i satisfies a target core temperature Ttarg when the food item exits the oven. Here, te,i is the end time when the food item exits the oven. The target core temperature is set by the USDA and/or the FDA.
The second approach is to ensure that the accumulated lethality Fi delivered to each food item i over the time interval [tb,i, te,i] satisfies a target lethality Ftarg. Here, tb,i is the begin time when the food item enters the oven. The target lethality is also set by the USDA and/or the FDA. The belt speed and the cooking temperatures in the oven are then scheduled so that each food item will have a scheduled temperature-time profile that delivers an accumulated lethality to the core of the food item which satisfies the target lethality.
As is well known, the accumulated lethality Fi delivered to a food item Fi over a particular time interval [tk,i, tm,i] is given by:                               F          i                =                              ∫                          t                              m                ,                i                                                    t                              k                ,                i                                              ⁢                                    10                                                (                                                                                                              T                          c                                                ⁡                                                  (                          t                          )                                                                    i                                        -                                          T                      REF                                                        )                                /                z                                      ⁢                          ⅆ              t                                                          (        1        )            
where tm,i and tk,i are respectively the begin and end times of the time interval [tm,i, tk,i], Tc(t)i is the core temperature-time profile for the core of the food item i, z is the thermal characteristic of particular pathogens to be destroyed during the time interval [tm,i, tk,i], and TREF is a reference temperature for destroying the pathogens. Thus, for each food item i being cooked, the accumulated lethality Fi delivered to the core of the food item i over the actual time interval [tb,i, te,i] while in the oven is given by this lethality equation, where tb,i=tm and is the begin time when the food item enters the oven and te,i=tk is the end time when the food item leaves the oven.
The belt speed and the cooking temperatures are scheduled off-line (i.e., prior to the start of the continuous oven cooking process) based on the target temperature Ttarg and/or the target lethality Ftarg. This provides a scheduled temperature-tune profile for each food item i that results in the final core temperature Tc(te,i)i of the food item at the end time te,i satisfying the target temperature and/or that results in an accumulated lethality Fi over [tb,i, te,i] being delivered to the food item that satisfies the target lethality.
However, it is common to have a process deviation during a continuous oven cooking process. This may occur when the actual cooking temperature, the actual air circulation velocity, and/or the actual relative humidity in a zone of the oven drops below the corresponding scheduled cooking temperature, the scheduled air circulation velocity, and/or the scheduled relative humidity for the zone. Such a deviation will effect the fmal core temperature Tc(te,i)i of each food item i in the zone since this temperature is dependent on the actual environment temperature, the actual air circulation velocity, and the actual relative humidity. Furthermore, the accumulated lethality Fi over [tb,i, te,i] delivered to each food item i is also effected since, as is evident from Eq. (1) given earlier, this lethality is based on the core temperature of the food item.
Since each food item i in a continuous oven cooking process will have a unique temperature-time profile, the final core temperature Tc(te,i)i and the accumulated lethality Fi over [tb,i, te,i] is different for each food item i. This makes it difficult to identify, while on-line and in real time, each food item that will have a final core temperature below the target core temperature Ttarg and/or each food item that will have a predicted minimum total lethality delivered to it that is below the target total lethality Ftarg. As a result, the development of a controller that provides on-line handling of deviations in a continuous oven cooking process without stopping the belt of the oven has to date not been developed.
In summary, the present invention comprises a continuous oven cooking system, a controller for use in the continuous oven cooking system, and a method performed by the controller. The system, controller, and method are used to administer a continuous oven cooking process performed on a line of food items and provide on-line handling of a deviation in a scheduled parameter during the process. In addition to the controller, the continuous oven cooking system includes an oven through which the food items are conveyed.
The controller controls the oven in performing the continuous oven cooking process according to scheduled parameters. When a deviation below a specific scheduled parameter occurs, the controller identifies those of the food items that will in response have (a) an accumulated lethality predicted to be delivered to them during the continuous oven cooking process that is less than a target lethality, or (b) have a core temperature at the end of the continuous oven cooking process that is less than a target core temperature. This specific scheduled parameter may be a scheduled environment temperature, scheduled air circulation velocity, or scheduled relative humidity in a cooking zone of the oven through which the line of containers is conveyed. It also may be a scheduled initial core temperature for the food items or a scheduled belt speed for a belt conveying the containers in line through the oven.